A known device for the implementation of the method described above is the product "Articulograph AG100" made by Carstens Medizinelektronik GmbH, Gottingen, Germany, which was developed in collaboration with the University of Gottingen. This known device is used to register the speech movements in the oral cavity having a helmet on which three reference coils are arranged. The reference coils are aligned perpendicular and parallel to each other in a measuring plane. Ideally, the measuring plane coincides with the center plane of the head of a person wearing the helmet. The oral cavity of the head is spaced at an approximately equal distance from all three reference coils in this case. The three reference coils are used to generate three different alternating magnetic fields, which are distinguishable by different frequencies. A coil used as a directionally sensitive magnetic field sensor is attached in the oral cavity, for example to the tongue of the person wearing the helmet, the spatial arrangement of which is registered, in order to register the speech movements of the person wearing the helmet. The alternating voltage induced in the coil by the alternating magnetic fields of the reference coils is then measured with the aid of a measuring device. The measuring device distinguishes and separates the alternating voltages induced by the individual alternating magnetic fields by their frequencies. An evaluation device is also provided which determines the spatial arrangement of the coil in the oral cavity from the measured alternating voltages. At first the distance between the coil and the respective reference coils is determined from the absolute values of the individual induced voltages. A position vector results from the three distances of the coil to the three reference coils in the oral cavity. The position vector is actually overdetermined by this, as long as it lies in the center plane of the head of the person wearing the helmet, i.e. in the measuring plane, in which the three reference coils are arranged. In principle two reference coils would suffice to determine the position vector of the coil in this plane. This is only valid, though, as long as the coil in the oral cavity is aligned exactly parallel with respect to the reference coils. As soon as the coil has a direction vector diverging from this position, the alternating voltage induced in the coil decreases in spite of an unchanged distance to the reference coils which the measuring unit cannot distinguish from an increasing distance of the coil to the reference coils. But since the supposed distance of the coil to all three reference coils increases by the same factor as a result of this tilting, a compensation of this factor in the known device for registering speech movements, by the overdetermination described above, is possible. As long as an exact parallel alignment of the coil to the reference coils would be ensured, a lateral deviation of the coil from the measuring plane could be observed with this known device. This would cause a relatively large error, though, since the distance of the coil to the reference coils varies only slightly during a movement perpendicular to the measuring plane.